The present invention relates to a golf club head in which a fringe portion of a face member is fixed to a head body by welding.
As compared with conventional golf club heads, with recent golf club heads, the volume of the head has become large for the ease of striking the ball and to improve stability and increase the flying distance. Since such a golf club head is so configured as to increase the volume of the head while avoiding the tendency of the club head becoming heavy, the respective portions of the head in terms of thickness are formed to be thin, and metallic materials having fixed thicknesses are in many cases used for the respective portions of the head. For example, in the case of a face, a face member is used which is processed into a plate member with a uniform thickness made of a metal such as a titanium alloy. According to the face member constituted by such a plate member with a uniform thickness, it is possible to thin the overall face member in terms of its thickness without unevenness in the overall thickness and strength, so that it is possible to obtain a stable-quality face excelling in repulsion.
In contrast to the conventional golf club head in which the thickness of the overall face member is fixed, a golf club head has been recently introduced in which a thick-walled portion and a thin-walled portion are provided in the face member, and the thickness of the face member is varied for the respective portions so as to optimally distribute the rigidity (JP-A-9-239075).
According to the golf club head in which a central portion of the face member is made thick and its peripheral portion is made thin, it is possible to obtain a ball striking surface in which the central portion has high rigidity, is difficult to flex at the moment of impacting, and can strike the ball stably. Meanwhile, the peripheral portion is low in rigidity, flexes and rebounds, thereby making it possible to increase the flying distance of the ball.
However, since the face members of the conventional type in which the thickness is varied for the respective portions are fabricated by forging, variations of the thickness of the face members and their waviness are large, so that it is difficult to fabricate the respective portions with planned dimensions and strengths. In particular, since the peripheral portion is formed with a small thickness, apprehension concerning the strength remains.
JP-A-11-76474 proposes a golf club head in which a face member obtained by subjecting a metal member such as a titanium alloy to rolling is used to enhance the strength and ball rebounding performance.
However, since the metallic face member subjected to rolling is a metal plate member having a uniform thickness in its entirety, and the variations of the strength of the respective portions are small, if the face member is made thin, the central portion of the face is easily flexed at the instant of impacting, and sufficient rebounding can be obtained by the overall face, but the strength of the central portion of the face for directly hitting the ball cannot be sufficiently obtained. At the same time, it is difficult to form a stable striking surface. In addition, the striking feel at the time of impacting is not clear.
Meanwhile, JP-A-9-239075 proposes a golf club head in which a metallic face member is formed by forging, and a central portion is made thick, and its peripheral portion is made thin. With the face member in which a thick-walled portion and a thin-walled portion are formed by this forging has an advantage in that it is possible to obtain a striking surface in which the central portion of the face has sufficient strength.
However, since the face member is formed in such a form that there are variations in the thickness since the central portion is made thick and the peripheral portion of the face is made thin by forging, there are large variations in quality. For example, it is impossible to obtain a planned configuration, and variations in the strength are large. In particular, variations in the strength are likely to occur in the thin-walled portion. Accordingly, there has been a tendency that breakage is likely to start from the thin-walled portion where the variations in the strength are large.
In a metallic golf club head, the directionality of a struck ball is improved by increasing the moment of inertia, and that the flying distance is improved with a high rebound of the ball by making the face thin-walled. Golf clubs have been actually marketed to which are fitted golf club heads in which, concerning such faces, the strength is partially enhanced, the rebounding is partially enhanced, and a thick-walled portion and a thin-walled portion are partially provided to make uniform the stress of the face with respect to the impact. Such golf club heads have been introduced in JP-A-9-168613, JP-A-10-137372, JP-A-9-192273, and the like.
A metal face whose thickness is varied in the conventional golf club head is fabricated by casting or forging from a metal mass (round bar). In this case, if the metal face whose thickness is varied is fabricated by casting, the metallographic structure becomes coarse, and voids are likely to be produced, so that variations are likely to occur in the strength. In addition, if such a metal face is fabricated by forging from a metal mass, since large plastic deformation takes place, the metallographic structure becomes dense, but its density is not stable, and variations occur in the density of the structure. Moreover, since the metal face is normally manufactured by hot forging, the characteristics of the material undergo a change, so that the durable strength declines.
Thus the conventional metallic face which has been fabricated by casting or forging and whose thickness is varied has a problem in that there are variations in the strength, and breakage or the like is likely to occur.